The present invention relates to a method of recovering heat values from vitiated gaseous mixtures. More specifically, the present invention relates to a method of burning a supplemental fuel and simultaneously recovering heat values from vitiated gaseous mixtures, including sensible heat and the heat of combustion of any combustibles in the vitiated gaseous mixture.
Numerous manufacturing operations produce large quantities of hot, vitiated gaseous mixtures containing significant amounts of oxygen, combustibles, such as carbon monoxide, unburned fuels and carbon, or both oxygen and combustibles together with inert diluents. In addition, many of such manufacturing operations also require substantial amounts of fuel for process heating, the production of steam, etc. When fuels are relatively abundant and prices relatively low, it was common practice to vent the vitiated gaseous mixtures. This practice obviously wasted the sensible heat of such vitiated gaseous mixtures as well as the heat values which could be recovered by burning the combustibles. In addition, to the extent that the vitiated gaseous mixtures contained significant amounts of combustibles, such venting also contributed significantly to air pollution. Accordingly, with diminished supplies of fuels, particularly petroleum based fuels, and the substantial increases in the cost of fuels, it is no longer economic to waste the heat values of such vitiated gaseous mixtures. Accordingly, it has been proposed that the heat values of vitiated gaseous mixtures be recovered by combining the vitiated gaseous mixture with a supplemental fuel and supplemental air and burning the mixture to produce heat for process heaters, steam boilers and the like. However, irrespective of the amounts of supplemental fuel and supplemental air added to certain vitiated gaseous mixtures, there are certain such mixtures which are below the flammability threshold and, therefore, will not burn and others which are above the flammability threshold and theoretically should burn, but are incapable of stable combustion and sustained combustion, i.e., are subject to flame-out. In addition, such suggested techniques themselves produce significant amounts of air pollutants, including NO.sub.x, CO, carbon, unburned fuels, etc. In fact, in many cases, the method utilized to recover the heat values from the vitiated gaseous mixtures is equally as inefficient as the processes which produced the vitiated gaseous mixtures.